1. Field of the Invention
The present invention relates generally to a liquid crystal display device and a method of driving the same, and more particularly to an active-matrix liquid crystal display device and a method of driving the same.
2. Description of the Related Art
In recent years, mobile products in which liquid crystal panels are built, such as small-sized game machines, portable PCs and mobile phones, have been quickly gaining in popularity.
In general, the liquid crystal display panel is configured such that a liquid crystal layer is held between an array substrate and a counter-substrate. In the case where the liquid crystal display panel is of an active matrix type, the array substrate includes a plurality of pixel electrodes which are arranged substantially in a matrix, a plurality of gate lines which are disposed along rows of the plural pixel electrodes, a plurality of source lines which are disposed along columns of the plural pixel electrodes, and a plurality of pixel switching elements which are disposed near intersections of the plural gate lines and plural source lines.
The respective gate lines are connected to a gate driver which drives the gate lines. The respective source lines are connected to a source driver which drives the source lines. The gate driver and source driver are controlled by a control circuit.
Each of the switching elements is composed of, e.g. a thin-film transistor (TFT). When the associated gate line is driven by the gate driver, the switching element is rendered conductive, thereby applying a pixel voltage, which is set on the associated source line by the source driver, to the associated pixel electrode. The counter-substrate is provided with a common electrode which is opposed to the plural pixel electrodes disposed on the array substrate.
A liquid crystal pixel is constituted by a pair of each pixel electrode and the common electrode, together with a pixel region which is a part of the liquid crystal layer that is interposed between these paired electrodes. A driving voltage for the pixel is a difference between a pixel voltage, which is applied to the pixel electrode, and a counter-voltage which is applied to the common electrode. Even after the switching element is turned off, the driving voltage is retained between the pixel electrode and the common electrode.
Alignment of liquid crystal molecules in the pixel region is set by an electric field which corresponds to the driving voltage. Thereby, the transmittance of the pixel is controlled. The polarity inversion of the driving voltage is executed, for example, by cyclically reversing the polarity of the pixel voltage relative to the counter-voltage. Thus, the direction of electric field is reversed to prevent non-uniform distribution of liquid crystal molecules in the liquid crystal layer.
Attention has been paid to a field sequential method as a driving method of a liquid crystal panel. In the field sequential method, a color image is divided into, for example, an R (red) component, a G (green) component and a B (blue) component, and the respective components are sequentially displayed on the display panel in a time-division manner.
The field sequential method is characterized in that the light use efficiency is higher than in an ordinary color filter method. In the ordinary color filter method, since white backlight passes through RGB color filters, a loss occurs in light use efficiency. By contrast, since the field sequential method requires no color filter, no loss occurs, in principle, in the light use efficiency.
Moreover, in the field sequential method, there is no need to divide one pixel into sub-pixels of RGB, as in the color filter method. Thus, since the pixel aperture ratio can be made higher than in the color filter method, the occurrence of loss of light use efficiency can advantageously be suppressed. In the prior art, there has been proposed a liquid crystal display device which performs color liquid crystal display on a transmissive liquid crystal display panel that is of a normally black-and-white mode (see Jpn. Pat. Appln. KOKAI Publication No. 5-80717).
In a liquid crystal display device which adopts the field sequential method, in a case where column inversion or frame inversion is executed as a polarity inversion scheme, image quality may deteriorate, in some cases, due to a luminance gradient occurring in a display image.